This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Myosin is a motor protein that moves along actin filaments by using the energy generated in ATP hydrolysis. This energy transduction is thought to be causesd by the swinging motion of the lever arm portion of the myosin motor domain. The chemical energy of ATP is mechanically transmitted for the physical swing of the lever arm to occur like a cam-shaft motion through subdomain steric interactions. In the transmission mechanism, it is thought that the reactive cysteine (SH1-SH2) region plays an important role for such subdomain communication. The SH1-SH2 region is very flexible and has been identified as a fulcrum point. We have been incorporated the photochromic molecules, which can undergo a reversible configurational change by light/UV irradiation, into the SH1-SH2 region of of skeletal muscle myosin subfragment 1 (S1). Localized conformational change of myosin head induced by photoisomerization has been investigated with biochemical measurements. It is expected that the global conformational changes of the myosin motor in the photochromic transition can be observed by using a small angle x-ray scattering technique. The results will provide the relationship between the converter domain and the lever arm position as the mechanisn inducing the global conformation. In addition, we are planning to measure the stability of a myosin motor protein by a stoppped-flow X-ray scattering technique when the various kind of nucleotide analogs that mimick the intermediates of the ATPase cycle bind to it. This experiment will be done in collaboration with Dr. Hiroshi Kihara (Kansai Medical School, Japan) who will make a unfolding/folding experiments of proteins.